A. Field of the Invention
The present invention relates to a new and improved float employed with a data acquisition device to measure the fluid level in a reservoir and to a new and improved method for measuring fluid within a reservoir.
B. Description of the Prior Art
The measurement of the volume and level of fluid within a reservoir is most accurately accomplished through the use of sophisticated data acquisition devices and floats. Measurement of the distance the float travels within the reservoir from a selected point before contacting the surface of the fluid is performed and recorded by the data acquisition device.
One prior art procedure for measuring involves dropping the float with a tape attached to the float onto the fluid. The tape includes accurately punched holes. The holes in the tape are counted until the float is supported by the measured fluid, thus allowing a data acquisition device to measure the length of the tape and display the fluid volume and height.
Another prior art procedure utilizes a potentiometer whose shaft position is a function of the number of turns made by the measuring tape in unwinding from a reel as the float is lowered. Such a prior art procedure and system is disclosed in U.S. Pat. No. 3,855,585.
A substantial problem is employing floats in the above-described prior art procedures and particularly if measuring fluids particularly liquified gases within storage tanks on ocean going oil tankers, lies in replacing or repairing floats and/or measuring tapes when necessary, due to damage or malfunction. Conventional techniques involve draining the tank, and performing repairs after entering through an access port. In the case of liquified gases, the tank must be drained and warmed before entering for repairs or adjustments. It will be appreciated by those skilled in the art that these methods are cumbersome, expensive and time consuming. This relative motion of the surface of the fluid produces inaccuracies in reading as a result of friction and misalignment of the float on the guide wires that maintain the float in the desired alignment.
The conventional prior art solution to this problem is to contain the float, and measuring tape in a separate vertical tube that extends from the data acquisition device into the reservoir or tank. This tube is termed a stilling well. However, the construction of the stilling well is expensive and is subject to contamination by debris at the bottom of the tank or through communicating holes fabricated in the wall of the well. This contamination results in permanent or temporary differences between the level of fluid being measured and the actual level of fluid within the tank.
A further difficulty with a stilling well arises out of the use of a float in tanks containing liquified natural gas. Due to the low temperature of liquified natural gas and the subsequent vaporization, the float is often inaccurate. Moreover, the use of a stilling well at these low temperatures is additionally expensive.
Under these conditions and operating problems, it is highly desirable for operators of data acquisition devices to remove the float from the well and reintroduce it for periodic measurements. The float is stored in a benign environment between readings. This removal, however, is difficult due to the physical fact that the accuracy of the float is represented by an equation, that includes the cross-sectional area of the surface of the float that engages the fluid in the denominator of the equation. This physical fact necessitates a float of a relatively thin, flat construction thereby making withdrawal of the float during non-measurement periods extremely difficult. Typical prior art floats, for example, are of a disc-like configuration approximately one inch thick and often times as large as six inches in diameter.